Aluminum Chemical Properties,Uses,Production

Description

Aluminum is the third most abundant element in the crust of the earth, accounting for 8.13% by weight. It does not occur in free elemental form in nature, but is found in combined forms such as oxides or silicates. It occurs in many minerals including bauxite, cryolite, feldspar and granite. Aluminum alloys have innumerable application; used extensively in electrical transmission lines, coated mirrors, utensils, packages, toys and in construction of aircraft and rockets.

Production Methods

Most aluminum is produced from its ore, bauxite, which contains between 40 to 60% alumina either as the trihydrate, gibbsite, or as the monohydrate, boehmite, and diaspore. Bauxite is refined first for the removal of silica and other impurities. It is done by the Bayer process. Ground bauxite is digested with NaOH solution under pressure, which dissolves alumina and silica, forming sodium aluminate and sodium aluminum silicate. Insoluble residues containing most impurities are filtered out. The clear liquor is then allowed to settle and starch is added to precipitate.
The residue, so-called “red-mud”, is filtered out. After this “desilication,” the clear liquor is diluted and cooled. It is then seeded with alumina trihydrate (from a previous run) which promotes hydrolysis of the sodium aluminate to produce trihydrate crystals. The crystals are filtered out, washed, and calcined above 1,100°C to produce anhydrous alumina. The Bayer process, however, is not suitable for extracting bauxite that has high silica content (>10%). In the Alcoa process, which is suitable for highly silicious bauxite, the “red mud” is mixed with limestone and soda ash and calcined at 1,300°C. This produces “lime-soda sinter” which is cooled and treated with water. This leaches out water-soluble sodium alumnate, leaving behind calcium silicate and other impurites.
Alumina may be obtained from other minerals, such as nepheline, sodium potassium aluminum silicate, by similar soda lime sintering process.Metal aluminum is obtained from the pure alumina at 950 to 1000°C electrolysis (Hall-Heroult process). Although the basic process has not changed since its discovery, there have been many modifications. Aluminum is also produced by electrolysis of anhydrous AlCl3.
Also, the metal can be obtained by nonelectrolytic reduction processes. In carbothermic process, alumina is heated with carbon in a furnace at 2000 to 2500°C. Similarly, in “Subhalide” process, an Al alloy, Al-Fe-Si-, (obtained by carbothermic reduction of bauxite) is heated at 1250°C with AlCl vapor. This forms the subchloride (AlCl), the vapor of which decomposes when cooled to 800°C.

Physical properties

Chemical Properties

Aluminum is the most commonly available element in homes and workplaces. Aluminum
is readily available for human ingestion through the use of food additives, antacids, buffered aspirin, astringents, nasal sprays, and antiperspirants; from drinking water; from automobile exhaust and tobacco smoke; and from using aluminum foil, aluminum cookware,
cans, ceramics, and fi reworks. Aluminum toxicity and its association with Alzheimer’s
disease in humans require more studies. Some data are against and some are for, because
the evidences are inadequate and inconclusive to suggest aluminum as the primary cause
of the disease. Prolonged periods of exposure to aluminum and dust causes coughing,
wheezing, shortness of breath, memory loss, learning diffi culty, loss of coordination, disorientation, mental confusion, colic, heartburn, fl atulence, and headaches. Chronic exposures to alumina dust cause irritation to the eyes, skin, respiratory system, pulmonary
fi brosis, and lung damage

Chemical Properties

Aluminum metallic powder is a light, silvery-white to gray, odorless powder. Aluminum
metallic powder is reactive and flammable. Aluminum is normally coated with a layer of
aluminum oxide unless the particles are freshly formed. There are two main types of aluminum powder: the “fl ake” type made by stamping the cold metal and the “granulated”
type made from molten aluminum. Pyro powder is an especially fi ne type of “fl ake”
powder. Aluminum powders are used in paints, pigments, protective coatings, printing
inks, rocket fuel, explosives, abrasives, and ceramics; the production of inorganic and
organic aluminum chemicals; and as catalysts. Pyro powder is mixed with carbon and
used in the manufacture of fi reworks. The coarse powder is used in aluminothermics.

Chemical Properties

History

The ancient Greeks and Romans used alum in medicine
as an astringent, and as a mordant in dyeing. In 1761 de
Morveau proposed the name alumine for the base in alum,
and Lavoisier, in 1787, thought this to be the oxide of a still
undiscovered metal. Wohler is generally credited with having
isolated the metal in 1827, although an impure form was prepared
by Oersted two years earlier. In 1807, Davy proposed
the name alumium for the metal, undiscovered at that time,
and later agreed to change it to aluminum. Shortly thereafter,
the name aluminium was adopted to conform with the “ium”
ending of most elements, and this spelling is now in use elsewhere
in the world. Aluminium was also the accepted spelling
in the U.S. until 1925, at which time the American Chemical
Society officially decided to use the name aluminum thereafter
in their publications. The method of obtaining aluminum
metal by the electrolysis of alumina dissolved in cryolite was
discovered in 1886 by Hall in the U.S. and at about the same
time by Heroult in France. Cryolite, a natural ore found in
Greenland, is no longer widely used in commercial production,
but has been replaced by an artificial mixture of sodium,
aluminum, and calcium fluorides. Bauxite, an impure hydrated
oxide ore, is found in large deposits in Jamaica, Australia,
Suriname, Guyana, Russia, Arkansas, and elsewhere. The
Bayer process is most commonly used today to refine bauxite
so it can be accommodated in the Hall–Heroult refining
process used to make most aluminum. Aluminum can now
be produced from clay, but the process is not economically
feasible at present. Aluminum is the most abundant metal to
be found in the Earth’s crust (8.1%), but is never found free
in nature. In addition to the minerals mentioned above, it is
found in feldspars, granite, and in many other common minerals.
Twenty-two isotopes and isomers are known. Natural
aluminum is made of one isotope, 27Al. Pure aluminum, a silvery-
white metal, possesses many desirable characteristics.
It is light, nontoxic, has a pleasing appearance, can easily be
formed, machined, or cast, has a high thermal conductivity,
and has excellent corrosion resistance. It is nonmagnetic and
nonsparking, stands second among metals in the scale of malleability,
and sixth in ductility. It is extensively used for kitchen
utensils, outside building decoration, and in thousands of industrial
applications where a strong, light, easily constructed
material is needed. Although its electrical conductivity is only
about 60% that of copper, it is used in electrical transmission
lines because of its light weight. Pure aluminum is soft and
lacks strength, but it can be alloyed with small amounts of
copper, magnesium, silicon, manganese, and other elements
to impart a variety of useful properties. These alloys are of
vital importance in the construction of modern aircraft and
rockets. Aluminum, evaporated in a vacuum, forms a highly
reflective coating for both visible light and radiant heat. These
coatings soon form a thin layer of the protective oxide and do
not deteriorate as do silver coatings. They have found application
in coatings for telescope mirrors, in making decorative
paper, packages, toys, and in many other uses. The compounds
of greatest importance are aluminum oxide, the sulfate, and
the soluble sulfate with potassium (alum). The oxide, alumina,
occurs naturally as ruby, sapphire, corundum, and emery, and
is used in glassmaking and refractories. Synthetic ruby and
sapphire have found application in the construction of lasers
The Elements 4-3
for producing coherent light. In 1852, the price of aluminum
was about $1200/kg, and just before Hall’s discovery in 1886,
about $25/kg. The price rapidly dropped to 60￠ and has been
as low as 33￠/kg. The price in December 2001 was about 64￠/
lb or $1.40/kg.

Definition

ChEBI: An aluminium cation that has a charge of +3.

Uses

As pure metal or alloys (magnalium, aluminum bronze, etc.) for structural material in construction, automotive, electrical and aircraft industries. In cooking utensils, highway signs, fencing, containers and packaging, foil, machinery, corrosion resistant chemical equipment, dental alloys. The coarse powder in aluminothermics (thermite process); the fine powder as flashlight in photography; in explosives, fireworks, paints; for absorbing occluded gases in manufacture of steel. In testing for Au, As, Hg; coagulating colloidal solutions of As or Sb; pptg Cu; reducer for determining nitrates and nitrites; instead of Zn for generating hydrogen in testing for As. Forms complex hydrides with lithium and boron, such as LiAlH4, which are used in preparative organic chemistry.

General Description

Aluminum metal held above melting point of 1220°F (660°C) for ease in handling. Cools and solidifies if released. Contact causes thermal burns. Plastic or rubber may melt or lose strength upon contact. Protective equipment designed for chemical exposure only is not effective against direct contact. Take care walking on the surface of a spill to avoid stepping into a pocket of molten aluminum below the crust. Do not attempt to remove aluminum impregnated clothing because of the danger of tearing flesh if there has been a burn.

Air & Water Reactions

Violent reaction with water; contact may cause an explosion or may produce a flammable gas (hydrogen). Moist air produces hydrogen gas. Does not burn on exposure to air.

Reactivity Profile

ALUMINUM , MOLTEN, is a reducing agent. Coating moderates or greatly moderates its chemical reactivity compared to the uncoated material. Reacts exothermically if mixed with metal oxides and heated (thermite process). Heating a mixture with copper oxides caused a strong explosion [Mellor 5:217-19 1946-47]. Reacts with metal salts, mercury and mercury compounds, nitrates, sulfates, halogens, and halogenated hydrocarbons to form compounds that are sensitive to mechanical shock [Handling Chemicals Safely 1980. p. 135]. A number of explosions in which ammonium nitrate and powdered aluminum were mixed with carbon or hydrocarbons, with or without oxidizing agents, have occurred [Mellor 5:219 1946-47]. A mixture with powdered ammonium persulfate and water may explode [NFPA 491M 1991]. Heating a mixture with bismuth trioxide leads to an explosively violent reaction [Mellor 9:649 (1946-47)]. Mixtures with finely divided bromates(also chlorates and iodates) of barium, calcium, magnesium, potassium, sodium or zinc can explode by heat, percussion, and friction, [Mellor 2:310 (1946-47]. Burns in the vapor of carbon disulfide, sulfur dioxide, sulfur dichloride, nitrous oxide, nitric oxide, or nitrogen peroxide, [Mellor 5:209-212,1946-47]. A mixture with carbon tetrachloride exploded when heated to 153° C and also by impact, [Chem. Eng. News 32:258 (1954)]; [UL Bull. Research 34 (1945], [ASESB Pot. Incid. 39 (1968)]. Mixing with chlorine trifluoride in the presence of carbon results in a violent reaction [Mellor 2 Supp. 1: 1956]. Ignites in close contact with iodine. Three industrial explosions involving a photoflash composition containing potassium perchlorate with aluminum and magnesium powder have occurred [ACS 146:210 1945], [NFPA 491M 1991]. Is attacked by methyl chloride in the presence of small amounts of aluminum chloride to give flammable aluminum trimethyl. Give a detonable mixture with liquid oxygen [NFPA 491M 1991]. The reaction with silver chloride, once started, proceeds with explosive violence [Mellor 3:402 1946-47]. In an industrial accident, the accidental addition of water to a solid mixture of sodium hydrosulfite and powdered aluminum caused the generation of SO2, heat and more water. The aluminum powder reacted with water and other reactants to generate more heat, leading to an explosion that killed five workers [Case Study, Accident Investigation: Napp Technologies, 14th International Hazardous Material Spills Conference].

Hazard

Health Hazard

Finely divided aluminum dust is moderately flammable and explodes by heat or contact with strong oxidizing chemicals. Chronic inhalation of the powder can cause aluminosis, a type of pulmonary fibrosis. It is almost nontoxic by ingestion.

Health Hazard

Exposures to aluminum metallic powder have been known to cause health effects with
symptoms such as irritation, redness, and pain to the eyes, coughing, shortness of breath,
irritation to the respiratory tract, nausea, and vomiting in extreme cases. In prolonged
periods of inhalation exposures, as in occupational situations, aluminum metallic powder
is known to cause pulmonary fi brosis, numbness in fi ngers, and (in limited cases) brain
effects. Workers with pre-existing skin disorders, eye problems, or impaired respiratory
function are known to be more susceptible to the effects of aluminum metallic powder.

Health Hazard

Occupational exposure to aluminum dust and fumes during welding provide suggestive
evidence that there may be a relationship between chronic aluminum exposure and subclinical neurological effects, such as impairment on neurobehavioral tests for psychomotor and cognitive performance. Inhalation exposure has not been associated with overt
symptoms of neurotoxicity. Prolonged exposure to high concentrations of aluminum and
its accumulation causes disturbances in renal function, dialysis, and encephalopathy
syndrome—a degenerative neurological syndrome characterized by the gradual loss of
motor, speech, and cognitive functions

Fire Hazard

Substance is transported in molten form at a temperature above 705°C (1300°F). Violent reaction with water; contact may cause an explosion or may produce a flammable gas. Will ignite combustible materials (wood, paper, oil, debris, etc.). Contact with nitrates or other oxidizers may cause an explosion. Contact with containers or other materials, including cold, wet or dirty tools, may cause an explosion. Contact with concrete will cause spalling and small pops.

Potential Exposure

Most hazardous exposures to aluminum occur in smelting and refining processes. Aluminum is mostly produced by electrolysis of Al2O3 dissolved in molten cryolite (Na3AlF6). Aluminum is alloyed with copper, zinc, silicon, magnesium, manganese, and nickel; special additives may include chromium, lead, bismuth, titanium, zirconium, and vanadium. Aluminum and its alloys can be extruded or processed in rolling mills, wire works, forges, or foundries; and are used in the shipbuilding, electrical, building, aircraft, automobile, light engineering, and jewelry industries. Aluminum foil is widely used in packaging. Powdered aluminum is used in the paints and pyrotechnic industries. Alumina, emery, and corundum has been used for abrasives, refractories, and catalysts; and in the past in the first firing of china and pottery.

First aid

If this chemical gets into the eyes, remove any contact lenses at once and irrigate immediately for at least 15 minutes, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts the skin, remove contaminated clothing and wash immediately with soap and water. Seek medical attention immediately. If this chemical has been inhaled, remove from exposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if heart action has stopped. Transfer promptly to a medical facility. When this chemical has been swallowed, get medical attention. Give large quantities of water and induce vomiting. Do not make an unconscious person vomit.

storage

Aluminum metallic powder should be kept stored in a tightly closed container, in a cool, dry, ventilated area, protected against physical damage and isolated from sources of heat, ignition, smoking areas, and moisture. Aluminum metallic powder should be kept away from acidic, alkaline, combustible, and oxidizing materials and separate from halogenated compounds.

Incompatibilities

Aluminum powder forms an explosive mixture with air and is a strong reducing agent that reacts violently with oxidizers, strong bases; strong acids; somehalogenated hydrocarbons; nitrates, sulfates, metal oxides and many other substances. Keep away from combustible materials.

Waste Disposal

Consult with environmental regulatory agencies for guidance on acceptable disposalpractices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal of Aluminum Oxide-Disposal in a sanitary landfill. Mixing of industrial process wastes and municipal wastes at such sites is not encouraged however. Aluminum powder may be recovered and sold as scrap. Recycling and recovery is a viable option to disposal for aluminum metal and aluminum fluoride (A-57).

Precautions

The dry powder is stable but the damp or moist bulk dust may heat spontaneously and
form flammable hydrogen gas. Moist aluminum powder may ignite in air, with the formation of flammable hydrogen gas and a combustible dust. Powdered material may form
explosive dust-air mixtures. Contact with water, strong acids, strong bases, or alcohols
releases flammable hydrogen gas. The dry powder can react violently or explosively with
many inorganic and organic chemicals